If I wasn't in the spa industry, was younger and was looking for a spa I might conclude Infinity "looks decent" but I'd suspect it was because my eyes would be fixated on the price tag. In the end I think it's a spa that will cost twice as much per month to operate than a well insulated spa. That obviously depends on where you live but I'd plan on an extra $40 to $80/month depending on your situation so fator that in when you see the price tag.
I'd also expect it to be a haul away spa in 6 to 9 years depending on how much babysitting I'd want to do. At this point in my life I concentrate more on value than simply price tag so its not for me but for a true DIYer who wants to get his feet wet with his first spa I understand the appeal of the price tag and the fact that they've dressed it up enough to make it look ok (just like all new cars look nice but down the road the differences show...).
Here is a previous thread started by someone who services that type spa (which is made by Infinity in their Texas plant) that I think is informative on both sides with a couple owners chiming in who seem to understand what they purchased.
http://www.poolspaforum.com/forum/index.php?showtopic=10797
Value IS a function of the price tag. It's what you get in return for what is paid. Would I pay Costco's regular price for that tub? Probably not. Would I pay the sale price? Probably. I have been reading these threads, including the one you posted, for months now. As it's stated in other posts, it's like comparing a Kia to a BMW. How many people get a BMW for their first car? Other Infinity Spa owners with whom I have corresponded stated they have seen very little change in their electric bill (with added insulation) albeit they are in warmer climates like me. The particular link you posted discusses a Keys Backyard spa. Unless I misunderstood the Infinity rep, the Laguna and Sunpeak are manufactured in Johnson City TN. I was just stating my opinion on what I will probably choose, based on my own research. There are several people who are considering a Costco tub for their first purchase. I was sharing my initial experience with Infinity for those in the same situation as me. When I contacted Infinity, I received information from them instead of a "high pressure sales pitch" that I have received from my local dealers. With the information I received from them I was able to determine that the Costco tub, Laguna, (on sale at the time) was not the tub for me, and I didn't make the purchase.